U.S. patent application number 10/576105 was filed with the patent office on 2011-03-24 for plasma source of directed beams and application thereof to microlithography.
Invention is credited to Peter Choi.
Application Number | 20110068282 10/576105 |
Document ID | / |
Family ID | 34385275 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110068282 |
Kind Code |
A1 |
Choi; Peter |
March 24, 2011 |
Plasma source of directed beams and application thereof to
microlithography
Abstract
A method for generating radiation in a range of desired
wavelengths in a direction of emission is provided. According to
the method, initial radiation is produced by a radiation source,
the wavelengths thereof including the desired range, and the
initial radiation is filtered in such a way as to substantially
eliminate the initial radiation beams having a wavelength outside
the desired range. The inventive method is characterized in that
the filtering is carried out by setting up a controlled
distribution of the refractive index of the beams in a control
region through which the initial radiation passes, in such a way as
to selectively deviate the beams of the initial radiation according
to the wavelength thereof and to recover the beams having desired
wavelengths. The invention also relates to an associated
device.
Inventors: |
Choi; Peter; (Orsay,
FR) |
Family ID: |
34385275 |
Appl. No.: |
10/576105 |
Filed: |
October 18, 2004 |
PCT Filed: |
October 18, 2004 |
PCT NO: |
PCT/FR04/02656 |
371 Date: |
April 30, 2007 |
Current U.S.
Class: |
250/504R ;
250/503.1 |
Current CPC
Class: |
G03F 7/70575 20130101;
G03F 7/70958 20130101; G21K 1/06 20130101 |
Class at
Publication: |
250/504.R ;
250/503.1 |
International
Class: |
H05G 2/00 20060101
H05G002/00; G01J 1/00 20060101 G01J001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 17, 2003 |
FR |
0312202 |
Claims
1. A process for generating, in a given direction of emission,
radiation in a desired range of wavelengths, said process
comprising: producing beams of initial radiation by a radiation
source whose wavelengths include the desired range, filtering the
beams of initial radiation to substantially eliminate the beams of
initial radiation whose wavelength is outside the desired range,
wherein said filtering is effected by introducing a controlled
distribution of the refraction index of the beams in a control
region that is traversed by the initial radiation to selectively
deflect the beams of the initial radiation according to their
wavelength, and to recover the beams of a desired wavelength.
2. A process according to claim 1 wherein the controlled
distribution of the refraction index of the beams is obtained by
controlling electron density distribution in the control
region.
3. A process according to claim 2 wherein the control region is
located in a plasma.
4. A process according to claim 3 wherein the plasma containing the
control region is itself contained in a chamber associated with the
radiation source.
5. A process according to claim 4 wherein electron density control
is effected to obtain an electron density which is greater at a
distance from a median initial radiation emission line than it is
on the median initial radiation emission line.
6. A process according to claim 5 wherein the median initial
radiation emission line is a straight initial radiation line, and
the initial radiation is produced by the radiation source with a
generally axi-symmetrical distribution around the straight initial
radiation line.
7. A process according to claim 6 wherein to obtain the electron
density distribution, an input of energy is applied to the plasma
along the median emission line of the initial radiation.
8. A process according to claim 7 wherein the input of energy is
effected by ionization of the plasma along the median emission line
of the initial radiation.
9. A process according to claim 8 wherein effecting the ionization,
comprises: establishing an electric voltage at the terminals of the
chamber containing the plasma, the terminals being spaced according
to the direction generally defined by the median emission line of
the initial radiation, and applying an energy beam to the median
initial radiation emission line.
10. A process according to claim 1 wherein, in order to recover the
beams of a desired wavelength, there is at least one window
downstream of the control region to selectively pass beams in the
desired wavelength range.
11. A process according to claim 10 wherein each window is
positioned on the median initial radiation emission line, with a
curvilinear abscissa corresponding to the place of intersection of
the beams in the desired wavelength range which were deflected with
the median initial radiation emission line.
12. A process according to claim 11 wherein the desired range of
wavelengths falls within the interval [0-100 nm].
13. A process according to claim 12 wherein the desired range of
wavelengths falls within the EUV spectrum.
14. A device for the generation of radiation in a desired range of
wavelengths, in a given direction of emission, where the device
comprises: a source of initial radiation whose wavelengths include
the desired range, filtering resources of the initial radiation, to
substantially eliminate the beams of initial radiation whose
wavelength is outside the desired range, wherein said filtering
resources include means to introduce a controlled distribution of
the refraction index of the beams in a control region that is
traversed by the initial radiation, to selectively deflect the
beams of the initial radiation according to their wavelength, and
to recover the beams of a desired wavelength.
15. A device according to claim 14 wherein said means to introduce
a controlled distribution of the refraction index comprises
resources to control the electron density distribution in the
control region.
16. A device according to claim 15 wherein the control region is
located in a plasma.
17. A device according to claim 16 wherein said plasma containing
the control region is itself contained in a chamber associated with
said radiation source.
18. A device according to claim 17 wherein said resources to
control the electron density distribution can achieve an electron
density which is greater at a distance from a median initial
radiation emission line than it is on the median initial radiation
emission line.
19. A device according to claim 18 wherein the median initial
radiation emission line is a straight initial radiation line, and
said resources to control the electron density distribution can
achieve an electron density that is generally axi-symmetrical
around the straight initial radiation line.
20. A device according to claim 19 wherein said resources to
control the electron density distribution include resources for
injecting energy into said plasma along the median initial
radiation emission line.
21. A device according to claim 20 wherein said resources for
injecting energy includes resources for ionization of the plasma
along the median initial radiation emission line.
22. A device according to claim 21 wherein said resources for
injecting energy comprise resources to: establish an electric
voltage at the terminals of the chamber containing the plasma, the
terminals being spaced in the general direction defined by the
median initial radiation emission line, and apply an energy beam to
the median initial radiation emission line.
23. A device according to claim 14 comprising, downstream of the
control region, at least one window to selectively pass beams in
the desired wavelength range.
24. A device according to claim 23 wherein each window is
positioned on the median initial radiation emission line, with a
curvilinear abscissa corresponding to a place of intersection of
the beams in the desired wavelength range which were deflected with
the median initial radiation emission line.
25. A device according to claim 24 wherein the device includes an
additional multi-layer filtration mirror in association with at
least some windows.
26. A device according to claim 25 comprising a multiplicity of
modules which each include a source of initial radiation and
associated filtering resources, and an optical resource useable to
collect the radiation subjected to filtration, in order to
re-direct it outside of the device.
27. A device according to claim 26 wherein said optical resource is
a multi-layer mirror which can finalize filtration of the
radiation.
28. A device according to claim 14 wherein the desired range of
wavelengths falls within the interval [0-100 nm].
29. A device according to claim 28 wherein the desired range of
wavelengths falls within the EUV spectrum.
30. A lithography device that includes a generation device
according to claim 29.
31. A process according to claim 3 wherein electron density control
is effected to obtain an electron density which is greater at a
distance from a median initial radiation emission line than it is
on the median initial radiation emission line.
32. A process according to claim 31 wherein the median initial
radiation emission line is a straight initial radiation line, and
the initial radiation is produced by the radiation source with a
generally axi-symmetrical distribution around the straight initial
radiation line.
33. A process according to claim 32 wherein to obtain the electron
density distribution, an input of energy is applied to the plasma
along the median emission line of the initial radiation.
34. A process according to claim 33 wherein the input of energy is
effected by ionization of the plasma along the median emission line
of the initial radiation.
35. A process according to claim 1 wherein the desired range of
wavelengths falls within the interval [0-100 nm].
36. A process according to claim 35 wherein the desired range of
wavelengths falls within the EUV spectrum.
37. A device according to claim 16 wherein said resources to
control the electron density distribution can achieve an electron
density which is greater at a distance from a median initial
radiation emission line than it is on the median initial radiation
emission line.
38. A device according to claim 37 wherein the median initial
radiation emission line is a straight initial radiation line, and
said resources to control the electron density distribution can
achieve an electron density that is generally axi-symmetrical
around the straight initial radiation line.
39. A device according to claim 38 wherein said resources to
control the electron density distribution include resources for
injecting energy into said plasma along the median initial
radiation emission line.
40. A device according to claim 39 wherein said resources for
injecting energy includes resources for ionization of the plasma
along the median initial radiation emission line.
41. A device according to claim 40 wherein said resources for
injecting energy comprise resources to: establish an electric
voltage at the terminals of the chamber containing the plasma, the
terminals being spaced in the general direction defined by the
median initial radiation emission line, and apply an energy beam to
the median initial radiation emission line.
42. A device according to claim 23 wherein the device includes an
additional multi-layer filtration mirror in association with at
least some windows.
43. A device according to claim 42 comprising a multiplicity of
modules which each include a source of initial radiation and
associated filtering resources, and an optical resource useable to
collect the radiation subjected to filtration, in order to
re-direct it outside of the device.
44. A device according to claim 43 wherein said optical resource is
a multi-layer mirror which can finalize filtration of the
radiation.
45. A lithography device that includes a generation device
according to claim 14.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to the generation of radiation at a
desired wavelength.
[0003] More precisely, this invention relates to a process for the
generation in a given direction of radiation emissions in a desired
range of wavelengths, where the process includes: producing initial
radiation by a radiation source whose wavelengths includes the
desired range; and filtering the initial radiation, to
substantially eliminate the part of the initial radiation whose
wavelength is outside the desired range.
[0004] The invention also relates to a radiation generating device
that can be used to implement such a process, as well as a
lithography device incorporating such a generation device.
[0005] 2. Discussion of Related Art
[0006] Processes and devices similar to the type mentioned above
are known.
[0007] One (non-limiting) example of implementation concerns the
generation of radiation at a desired wavelength intended for an
optical chain, for lithography applications on a photosensitive
substrate. FIG. 1 diagrammatically illustrates an optical system
100, that includes the following in succession:
[0008] a generator 10 of radiation in a desired range of
wavelengths;
[0009] a lens assembly 11 which receives the radiation coming from
the generator 10 and processes it (e.g., by subjecting it to
collimation and/or focusing of its beams);
[0010] a mask 12 which receives the processed radiation coming from
the lens assembly 11, and selectively allows to pass only the beams
arriving at the mask via a transmission pattern 120, with the
remainder of the radiation being stopped by the mask; and
[0011] a substrate 13 which receives the beams that have been
transmitted by the mask, and whose surface exposed to the radiation
bears a photo-resistant or photosensitive product.
[0012] The beams arriving at the substrate react with the product
and thus form, on the surface of the substrate, a pattern that
matches the transmission pattern of the mask.
[0013] The desired range of wavelengths of the generator 10 can in
particular be located in the ultra-violet (UV) spectrum, or in the
extreme UV (EUV) spectra.
[0014] Note that in this text, the term "EUV" is conventionally
used to refer to both EUV beams and soft x-rays.
[0015] The EUV beams are associated with very short wavelengths
(wavelengths less than 100 nm, and of the order of a few tens of
nms for example, where an application corresponds to a wavelength
of 13.5 nm). This is advantageous in particular for
photolithography applications, since in a corresponding manner, the
patterns drawn by the beams can be of very small dimensions. In
particular, this allows the formation of a larger quantity of
patterns on a substrate of the same size.
[0016] It is necessary however to associate radiation filtering
resources with the radiation generator.
[0017] In certain embodiments, in particular for radiation
generators whose wavelength is in the EUV range, the generator
includes a radiation source of the plasma source type.
[0018] In addition to the desired radiation, such radiation sources
also emit: radiation whose wavelengths do not correspond to the
desired range; and/or solid debris resulting from the interaction
between the plasma and solid parts of the chamber in which this
plasma is located (target, walls of the chamber, etc.).
[0019] In order to isolate, in the radiation coming from the source
of the generator, only the beams that are at a desired wavelength,
it is therefore necessary to provide filtering resources downstream
of the source (e.g., immediately downstream of the source, in order
to avoid exposing the mask to debris which could damage it).
[0020] In a known manner, such filtering resources include a
multi-layer mirror which selectively reflects the beams according
to their wavelength. Such a multi-layer mirror thus functions as a
band-pass filter. Such a multi-layer mirror does not pass on the
undesirable debris which can be emitted by the source, so that the
elements located downstream of the filtering resources are not
exposed to such debris. Such a solution allows filtering out of the
beams emitted by a radiation source that can produce such debris.
However, one drawback associated with such a known configuration is
that the debris emitted by the source can damage the mirror of the
filtering resources.
[0021] It would be possible to envisage distancing the filtering
resources from the source, so as to reduce the probability that
debris will damage the mirror of these filtering resources.
[0022] In this case however, there would be a significant reduction
in the radiation stream recovered by the filtering resources, thus
adversely affecting the performance of the whole optical
system.
[0023] It therefore appears that the known configurations for
generating radiation at a desired wavelength are associated with
drawbacks when the radiation source can generate debris.
[0024] In particular, this disadvantage concerns applications in
which the desired wavelengths fall in the EUV area.
SUMMARY OF THE INVENTION
[0025] One object of the invention is to provide processes and
devices that avoid these drawbacks.
[0026] In order to attain this objective, the invention proposes,
according to one embodiment, a process for the generation, in a
given emission direction, of radiation in a desired range of
wavelengths, where the process includes:
[0027] producing beams of initial radiation by a radiation source,
whose wavelengths include the desired range; and
[0028] filtering of the initial radiation, so as to substantially
eliminate the beams of the initial radiation whose wavelength is
outside the desired range, wherein the filtering is achieved by
introducing a controlled distribution of the refraction index of
the beams in a control region that is traversed by the initial
radiation, to selectively deflect the beams of the initial
radiation according to their wavelength, and to recover the beams
of a desired wavelength.
[0029] Preferred, though not limiting, aspects of such a process
are:
[0030] the controlled distribution of the refraction index of the
beams is obtained by controlling the density distribution of
electrons in the control region;
[0031] the control region is located in a plasma;
[0032] the plasma containing the control region is itself contained
in a chamber associated with the radiation source;
[0033] electron density control is effected to obtain an electron
density which is greater at a distance from a median initial
radiation emission line than it is on the median emission line of
the initial radiation;
[0034] the median initial radiation emission line is a straight
initial radiation line, and the initial radiation is produced by
the radiation source with a generally axi-symmetrical distribution
around the straight initial radiation line;
[0035] in order to obtain the electron density distribution, an
input of energy is applied to the plasma along the median initial
radiation emission line; and
[0036] the energy input is effected by ionization of the plasma
along the median initial radiation emission line.
[0037] In certain embodiments, in order to effect the ionization,
the following operations are required:
[0038] establishment of an electrical voltage at the terminals of
the chamber containing the plasma, the terminals being spaced in
the general direction defined by the median initial radiation
emission line;
[0039] application of an energy beam to the median initial
radiation emission line;
[0040] in order to recover the beams of a desired wavelength, there
is at least one window downstream of the control region, to
selectively pass beams in the desired wavelength range;
[0041] each window is positioned on the median initial radiation
emission line, with a curvilinear abscissa corresponding to the
place of intersection of the beams in the desired wavelength range
which were deflected with the median initial radiation emission
line;
[0042] the desired range of wavelengths falls within the interval
[0-100 nm]; and
[0043] the desired range of wavelengths falls within the EUV
spectrum.
[0044] According to a second aspect, the invention also proposes a
device for the generation, in a given emission direction, of
radiation in a desired range of wavelengths, where the device
includes:
[0045] a source of initial radiation whose wavelengths include the
desired range; and
[0046] filtering resources of the initial radiation, to
substantially eliminate the beams of the initial radiation whose
wavelength is outside the desired range, wherein the filtering
resources include the means to introduce a controlled distribution
of the refraction index of the beams in a control region that is
traversed by the initial radiation, to selectively deflect the
beams of the initial radiation according to their wavelength, and
to recover the beams of a desired wavelength.
[0047] Preferred, though not limiting, aspects of such a device are
as follows:
[0048] the means to introduce a controlled distribution of the
refraction index includes resources to control the electron density
distribution in the control region;
[0049] the control region is located in a plasma;
[0050] the plasma containing the control region is itself contained
in a chamber associated with the radiation source;
[0051] the resources to control the electron density distribution
can achieve an electron density which is greater at a distance from
a median initial radiation emission line than it is on the median
initial radiation emission line;
[0052] the median initial radiation emission line is a straight
initial radiation line, and the resources to control the electron
density distribution can achieve an electron density that is
generally axi-symmetrical around the straight initial radiation
line;
[0053] the resources to control the electron density distribution
include resources for injecting energy into the plasma along the
median initial radiation emission line;
[0054] the resources for injecting energy include resources for
ionization of the plasma along the median emission line of the
initial radiation;
[0055] the resources for injecting energy include resources to:
[0056] establish an electrical voltage at the terminals of the
chamber containing the plasma, with the terminals being spaced in
the general direction defined by the median initial radiation
emission line; and [0057] apply an energy beam to the median
initial radiation emission line;
[0058] downstream of the control region, the device includes at
least one window to selectively pass beams in the desired
wavelength range;
[0059] each window is positioned on the median initial radiation
emission line, with a curvilinear abscissa corresponding to the
place of intersection of the beams in the desired wavelength range,
which were deflected with the median initial radiation emission
line;
[0060] the device includes an additional multi-layer filtration
mirror in association with at least some windows;
[0061] the device includes a multiplicity of modules, which each
include a source of initial radiation and associated filtering
resources, as well as an optical resource that can be used to
collect the radiation subjected to filtration, in order to
re-direct it outside of the device;
[0062] the optical resource is a multi-layer mirror which can
finalize filtering of the radiation;
[0063] the desired range of wavelengths falls within the interval
[0-100 nm]; and
[0064] the desired range of wavelengths falls within the EUV
spectrum.
[0065] The invention also concerns a lithography device that
includes a generation device according to one of the above
aspects.
[0066] Other aspects, objectives and advantages of the invention
will appear more clearly on reading the following description of
the invention, which is provided with reference to the appended
drawings on which, apart from FIG. 1 has already been described
above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] FIG. 1 is a schematic diagram illustrating an optical
system.
[0068] FIG. 2 is a schematic diagram of a radiation generator
according to the invention.
[0069] FIG. 3 is a similar representation, illustrating an electron
density distribution which is controlled in a particular manner in
the context of the invention.
[0070] FIG. 4 illustrates a particular method of implementation of
the invention with a multiplicity of radiation sources.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0071] FIG. 2 diagrammatically illustrates a radiation generator 20
according to the invention. This radiation generator includes a
chamber 21 which is generally closed but with one side 210 open to
let pass the beams emitted by the chamber.
[0072] The chamber 21 includes a source 211 that can produce an
initial radiation R0. Typically this is a source containing a
plasma.
[0073] The initial radiation includes beams whose wavelength
corresponds to a desired range of wavelengths. In a preferred but
not limiting embodiment of the invention, the desired range of
wavelengths falls within the interval [0-100 nm]. This desired
range of wavelengths can thus be located in the EUV spectrum. The
chamber 21 can thus produce initial radiation in which a
significant quantity of beams correspond to the desired wavelength
range.
[0074] As mentioned previously, it is possible however that
undesirable effects can be associated with the emission from the
source: the initial radiation can also contain beams whose
wavelengths do not correspond exactly to the desired range; and it
is also possible that the source 211 may emit a certain amount of
debris with the initial radiation.
[0075] In order to prevent these undesirable effects, the generator
20 includes resources for filtering the initial radiation. These
filtering resources can introduce a controlled distribution of the
refraction index of the beams in a control region 212 traversed by
the initial radiation, to selectively deflect the beams of the
initial radiation according to their wavelength. The beams of a
desired wavelength are then recovered (in particular using
resources which will be described in this text).
[0076] Such embodiment makes use of a physical principle similar to
that, for example, which causes the deflection of light beams in
the presence of a gradient of the refraction index of the air (the
particular case of air with high temperature gradients).
[0077] In the embodiment illustrated in FIG. 2, the control region
is located inside of the chamber itself 21. Note that it is also
possible for this control region to be located outside the chamber
21, downstream of the latter on the trajectory of the initial
radiation.
[0078] Control of the distribution of the refraction index in the
control region can be achieved by controlling the electron density
distribution in the control region. In this regard, it is possible
to exploit the relationship linking the refraction index .eta. to
the electron density n.sub.e:
[0079] .eta.=(1-n.sub.e/n.sub.c).sup.1/2, where n represents a
critical electron density value beyond which the beams are no
longer able to pass, since this value of n.sub.c is related to the
wavelength of the beams concerned.
[0080] Returning to the method of implementation illustrated in
FIG. 2, the control region 212 is therefore located in the chamber
21, and this control region is thus in the plasma associated with
the source 211.
[0081] Control of the electron density distribution in the control
region allows one to influence the trajectories of the different
beams of the initial radiation, according to the wavelength of
these beams. This is illustrated in FIG. 2, which shows two general
trajectories of two types of beam: beams of a first wavelength
.lamda.1, these beams have the trajectory R1; and beams of a second
wavelength .lamda.2, which is shorter than the first wavelength
.lamda.1, these beams have the trajectory R2.
[0082] In a preferred embodiment of the invention which is
illustrated here, an electron density distribution is established
in the control region such that the electron density is greater at
a distance from a median initial radiation emission line than it is
on the median initial radiation emission line.
[0083] The "median initial radiation emission line" corresponds, in
the embodiment shown in FIG. 2, to the straight line A. Note that
in the embodiment illustrated here, the chamber is typically in the
shape of a round cylinder, and that the initial radiation is
emitted with a generally axi-symmetrical distribution of the beams,
around line A.
[0084] The configuration of the electron density distribution
desired in this embodiment is illustrated diagrammatically in FIG.
3, which shows electron density curves.
[0085] In this figure, it can be seen that the electron density
value is greater at the edges of the chamber (distanced from line
A) than in the middle of this chamber (close to line A). It can
also be seen that the three electron density curves that are shown
diverge in the peripheral region of the chamber. Such an electron
density distribution is opposite to the electron density
distribution that can normally be observed in the chamber of a
radiation source. In the case of a chamber of known type, one
generally observes a higher density at the center of the
chamber.
[0086] The density configuration shown in FIG. 3 is therefore
specific, and it is created by design for the embodiment of the
invention described here. In order to create such an electron
density distribution in the control region, energy is injected into
the plasma of the chamber 21 along the line A. This input of energy
can be effected, for example, by a beam of electrons or by a laser
beam, directed into the control region along the axis defined by
line A. This input of energy is illustrated diagrammatically by
arrow E. It is used to ionize the plasma in the control region,
along line A.
[0087] Prior to this input of energy, it was possible to establish
an electric voltage at the terminals of the chamber containing the
plasma, the terminals being spaced along the general direction
defined by the median initial radiation emission line.
[0088] FIG. 3 diagrammatically represents such terminals 2121 and
2122. It is thus possible to create an electron density
distribution of the type shown in FIG. 3. Note that such a
distribution can be obtained by starting from a density
distribution of a known type, in which the density is higher at the
center of the chamber.
[0089] The input of energy and the ionization associated with it is
used in this embodiment to "invert" the density configuration, and
to obtain a higher density close to the peripheral walls of the
chamber.
[0090] FIG. 3 shows three density distribution curves as mentioned.
These three curves are generally coincident in the central region
of the chamber (close to line A), but have different values of
density close to the walls of the chamber. These three curves
correspond to successive states of the electron density
distribution, when ionization of the central zone of the control
region has been effected.
[0091] At the end of such an ionization, there can be an electron
density which is already higher at the periphery of the control
region.
[0092] If, however, one then allows the plasma thus ionized to
develop, this configuration will then become accentuated, and the
value of the density will again increase at the periphery. In fact
the high-density electrons present in great quantity at the
periphery of the chamber will have a tendency to cause the internal
walls of this chamber to melt, single layer of wall coating by
single layer of wall coating.
[0093] This melting leads to an additional input of electrons at
the periphery of the chamber, which still further increases the
electron density in this area.
[0094] FIG. 2 specifically represents a window 222 which is
positioned at the focal point of the beams on the trajectory R2.
This window corresponds to a resource for recovery of beams of a
desired wavelength, from amongst the beams of the initial
radiation.
[0095] It has been seen that the different beams emitted by the
initial radiation R0 were deflected in a different manner, by the
electron density distribution which existed in the control region,
according to their wavelength. This selective deflection causes the
beams associated with a given wavelength to converge toward a
specific point on line A, referred to herein as the "focal
point".
[0096] The position of the focal point on line A (a position that
can be defined by a curvilinear abscissa of a marker linked to the
line A) therefore depends on the wavelength associated with this
focal point.
[0097] FIG. 2 shows focal points F1 and F2 associated respectively
with the beams of trajectories R1 and R2.
[0098] The window 222 is thus positioned at focal point F2. The
function of this window is to allow to pass only the beams arriving
at line A generally at focal point F2 (that is the beams of
wavelength .lamda.2). To this end, window 222 includes an opening
2220 which is preferably centered on line A.
[0099] This window thus forms an advantageous resource for
recovering only the beams of a desired wavelength. It thus improves
filtration of the beams emitted by the initial radiation.
[0100] In this way, it is possible to have windows in any desired
position on line A, according to the wavelength that one wished to
isolate.
[0101] It can therefore be seen that the invention allows beams of
a desired wavelength (or at desired wavelengths, to be exact) to be
isolated in an efficient manner.
[0102] With respect to the invention, there is no exposing of a
filtration resource, such as a multi-layer mirror, to debris that
can damage it.
[0103] With respect to the invention, the fact that the desired
beams are recovered at a specific point toward which they were
deflected already allows a large part of any debris emitted by the
source 21 to be avoided.
[0104] Implementation of recovery resources such as a window allows
the quantity of debris to be reduced still further. The result is
that at the end of this filtration, there is very little or no
debris.
[0105] Note that downstream of the focal point of the beams that
need to be recovered, it is possible to create resources for
optical conditioning of the beam formed by these filtered
beams.
[0106] In particular, this optical conditioning can be a
collimation and/or a focusing process.
[0107] The recovered beam can therefore be sent directly toward a
lithography mask.
[0108] It is also possible to direct the recovered beam toward
additional filtering resources, if so desired. Such additional
filtering resources can include a multi-layer mirror like those
which constitute the filtering resources that are known
currently.
[0109] The layers of such a multi-layer mirror are designed (in
composition and thickness) so that the mirror selectively reflects
only the beams of a given wavelength (according to a condition
known as the Bragg condition, which links the reflectivity of the
mirror to the wavelength of the incident beams).
[0110] In this variant, several filtering resources are used in
series. The resource that is furthest upstream, which performs a
selective deflection of beams and their recovery, provides
protection for the resource furthest downstream (the multi-layer
mirror) from the debris emitted by the source.
[0111] Note finally that it is possible to implement the invention
in a device that includes a multiplicity of sources of initial
radiation, each associated with resources that can be used to
control a distribution of the refraction index in an associated
control region.
[0112] This mode of implementation is illustrated diagrammatically
in FIG. 4.
[0113] In this figure, a multiplicity of chambers 21i which are
similar to the chamber 21 already described, direct their
respective radiation along respective median lines Ai, which
converge toward a central optic 23. The central optic can thus
receive the beams emitted by one or more chambers 21i, according to
the chambers that are active.
[0114] The distance between the optic 23 and each chamber is
adjusted to select the radiation filtering wavelength associated
with each active chamber. It is also thus possible to cause beams
of different wavelengths, coming from different chambers, to arrive
at the optic 23. The optic 23 is able to redirect the received
beams toward the exterior, and therefore toward other optical
processing resources (such as a lithography mask) for example.
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